Force and machinery topics, multiple choice questions about force

1) Elastic deformation occurs, a certain limit, length.

2) Bullets. 3) When two objects in contact with each other are in relative motion or have a tendency to move relatively, a force will be generated on the contact surface that hinders the motion of the phase objects, which is called friction.

4) Fulcrum, power, resistance, power arm, resistance arm.

5) Power multiplied by power arm is equal to resistance multiplied by resistance arm, F1L1=F2L26) F=(1 2)G, F=(1 2) (G object + G moving + G rope) movable pulley is applicable, or there are two strands of rope applicable If there are three strands of rope, then 1 2 is changed to 1 3, and so on

7) Deformation, simple.

Question 6 seems like this

x=0 y1=

x= 3 at y2= (at the lowest point) the height change δh=mgδh=mv2-mvo2

v=√50 m/s

mgδh(max)=mv²/2

h(max)=

y3=y2+δh(max)=0

Corresponds to x=5 6

All four answers were wrong.

A: The soccer ball is subject to only one gravitational force in the air.

B: After the tennis ball flies out of the force (note that it is the last word after the flight), there is only one gravity, which is the same as A.

C: There is no force between A and B. There is no way to talk about the object of force and the object of force.

d: Force is the interaction between objects, there is an extraordinary force, which means that when it acts with other people (things) it can exert (burst) a large force. But it cannot be said that he has very great power in itself.

I don't have any pictures.

5. Ground car n 10, the action of the force between objects is a mutual force that can change the motion state of the object.

<> is almost exactly the same as this question, but in the opposite direction.

Answer B analysis: The definition of gravity is that the force on an object due to the attraction of the earth is called gravity, and gravitational force is the force generated by the attraction of two objects to each other is called gravitational force;

Judge b according to the concept of elasticity;

The main purpose of using machinery is to save effort, save distance or change the direction of force, but no machine can save work to judge c;

When a machine is used to do work, the work done by the machine on the object is useful and must be done, and this part of the work is called useful work; As long as the machinery is used, it is inevitable to lose a part of the work, such as the friction that exists in the operation of the machinery, and a part of the work must be consumed to overcome the friction, and this part of the work is called the extra work The sum of the useful work and the extra work is called the total work, and the percentage of the useful work in the total work is the mechanical efficiency

Answer: According to the definition of gravity and gravitation, gravity is the force produced by the gravitational pull of an object, but gravity is not gravitational so a false

According to the concept of elastic force, we feel the strong effect of rubber bands and rulers when we pull them, which is elastic force Elastic force is generated by the elastic deformation of the object Therefore b is correct

The use of movable pulleys can save effort, but it will not save work, so C is wrong

According to the definition of mechanical efficiency, it is the percentage of useful work to the total work, so the machinery is in good running condition, it also has extra work, so the mechanical efficiency is less than 1 so d error

Therefore, choose b Comments: This question mainly examines the concepts of gravity, gravitational force, and mechanical efficiency, and it is easy to confuse the concept when doing the question, and it is easy to make mistakes Mechanical work is labor-saving but will not save work, many students mistakenly think that they will save labor if they save labor, which is easy to cause errors in judgment